Recycling plans, injury rates and manufacturing plans were among the details parsed at a hearing of the Martha’s Vineyard Commission Thursday, as testimony began to wind down on a long-running review of the regional high school’s proposed athletic field renovation.

Thursday’s hearing marked the fourth in a lengthy public hearing process for the $7 million field renovation, which includes the installation of a synthetic turf field. The project is under review as a development of regional impact (DRI).

Previous hearings tackled architectural plans, an in-depth toxicology report and a seemingly endless stream of passionate public comment on both sides of the issue.

On Thursday, commissioners turned their attention to lingering questions about turf recycling and safety — two issues raised repeatedly by the project’s opponents.

Mark Curran of Tencate Grass, a turf manufacturing company, spoke on behalf of the high school about the company’s field recycling program. Mr. Curran said the grass field product is cradle-to-cradle certified, meaning it can be recycled to make more synthetic grass fields.

“We can guarantee that any synthetic turf field installed at Martha’s Vineyard Regional High School, can be recycled through our process,” Mr. Curran said, noting the company’s commitment to recycling the field at the end of its 25-year life at no additional cost to the high school.

He said the company currently recycles the products at a brand new facility in Europe, and plans to establish a similar U.S. facility in the coming years.

Eric Hughes, a representative from Brock USA, which manufactures shock pads and filling for synthetic turf, said his company’s shock pad panels had also received cradle-to-cradle certification. The wood chip filling used inside the turf is also sustainably harvested, he said.

On the issue of injury, Dr. David Halsey, a hospital orthopedic surgeon and MVRHS team physician brought on by the high school, refuted claims that turf fields caused higher rates of injuries for school-aged children. Dr. Halsey cited a dearth of peer-reviewed literature on high-school turf injuries, pointing instead to the well-documented injury rate on the high school’s current facilities.

“In the 31 years that I’ve been practicing as a sports medicine physician, I have witnessed in the last four and a half years a higher percentage of injuries per school student than I’ve seen before,” he said.

In a question-and-answer period that followed, commissioners dug into the three presentations, many directing questions to the turf manufacturers, and some expressing skepticism about their claims of recyclability.

“There’s always a desire to spin things in the best light and I think we have to be careful of greenwashing when we’re talking about recyclability,” said Ben Robinson. Commissioners Jeff Agnoli and Christine Todd wondered about the specific costs of recycling and the possibility of large energy expenditures.

The hearing included more public testimony as well.

Island parent Samatha Look urged the commission to reject the project, pointing to troubling findings raised by the various toxicology tests conducted in the review. Freedom Cartwright criticized the high school more broadly for its failure to promote environmental justice. Former commissioner Richard Toole weighed in too.

“[The project] goes against everything that the MVC has been fighting for since it was established,” Mr. Toole said. “Please do the right thing, do not approve this plan as currently proposed with artificial turf.”

But high school adjustment counselor Matt Malowski spoke emotionally about the project, citing the importance of sports for the Island’s underserved children and criticizing the review process which has dragged on for weeks.

“We essentially do not have any foster care for our teenagers on Martha’s Vineyard and no respite housing . . . but we have received seven years of debate,” said Mr. Malowski.

And as the fourth hearing wound to a close, others echoed Mr. Malowski in his critique, pointing to the abundant material presented during the review and urging the commission to begin their deliberation process.

“You have a very difficult job in front of you,” said high school committee member Mike Watts. “My ask is that you actually, really scrutinize what people tell you, and understand whether it is fact or opinion.”

The hearing was continued to a fifth and final session April 1.

In other business Thursday, commissioners voted to approve new regulations for the Cape Pogue district of critical planning concern (DCPC).

The DCPC amendment aims to expand the town’s ability to promulgate and enforce rules for the ecologically sensitive area, which was designated a DCPC by the commission in the 1980s.

The changes allow for adding the town harbor master and shellfish constable to the DCPC advisory committee, while a subgroup of the committee would be granted authority to establish additional management rules, following original guidelines.

An enforcement group made up of the harbor master, police department and building inspector office will also be given authority to enforce the rules.

Commissioner Fred Hancock proposed a language change to the regulations that would clearly restrict the new group’s rule-making power to issues of wildlife and recreation.

The change was approved, along with the amended DCPC.

The amendments will return to Edgartown voters for final approval at the annual town meeting in May.